Chemical-mechanical polishing (CMP) is a known technique for planarizing various structures on a thin film substrate. CMP is conventionally used to create a smooth, planar surface for intermediate processing steps of a thin film fabrication process. Specifically, various layers such as metallization layers are deposited and etched during the fabrication of thin film devices on a substrate. The layers are commonly subjected to CMP so that planar deposition of additional layers is achieved. CMP processing not only is used to planarize protruding surfaces, but also to remove undesirable residues that remain from other substrate processing steps.
CMP involves simultaneous chemically etching and mechanical polishing or grinding of a surface so that a combined chemical reaction and mechanical polishing removes a desired material from the substrate surface in a controlled manner. The resulting structure is a planarized substrate surface with the protruding surface topography leveled. CMP is typically performed by polishing a substrate surface against a polishing pad that is wetted with a slurry including an acidic or basic solution, an abrasive agent and a suspension fluid.
Thin film magnetic heads, which are constructed using advanced integrated circuit processing techniques, have been developed to improve performance of high density magnetic recording while reducing fabrication cost. Thin film magnetic heads are typically constructed using multiple substrate processing steps, including steps of deposition, etching and planarization of multiple insulative, conductive and magnetic layers. In a typical conventional thin film magnetic head fabrication process, on the order of thousands of thin film heads are formed on a six inch substrate. The substrate is subsequently diced into a large number, typically thousands, of individual thin-film heads. Each head is mounted individually, one-by-one on a head mounting block. Each mounted head is subjected to a lapping or grinding process to planarize each head, resulting in a planar, rectangular parallelepiped structure. Lapping is a method of reducing the thickness of a substrate slice for applications in which accuracy of the substrate thickness is important to the operation of the device. After lapping processing, a slurry of water and fine grit is used to wear down the back of the slice. The slurry is placed between a flat plate and the back of the slice and the slice is moved with respect to the plate to mechanically remove the substrate material.
The individual lapping of each thin film magnetic head, one-by-one, is tremendously time consuming, greatly raising the cost of each thin film head and the cost of a recording and playback apparatus using thin film heads. For example, a typical wafer may contain sixteen thousand devices. The layer to be ground is typically only a few microns thick requiring a skilled artisan using a high degree of care to successfully grind the devices. Therefore, waste is common and grinding time for planarization a single device is often in the range of ten minutes so that grinding even a single wafer using a single grinder is clearly impractical. Furthermore, each grinder costs in the range of several hundred thousand dollars so that cutting a single wafer into multiple sections and grinding the sections on separate grinders does not improve the practicality of planarizing the devices by grinding. In addition, wheels for a grinder are expensive diamond wheels that cost approximately $3000 each and, although somewhat durable, do wear with repeated grindings.
These considerations indicate the high cost and time consuming nature of planarization via grinding.
In some processes, the thousands of thin film heads are constructed using multiple processing steps, similar to the processing steps of integrated circuit manufacture. The substrate is then sliced into rows to produce strips typically holding ten to sixteen devices. A row tool is the used, applying a rocking or lapping motion to planarize the multiple heads in a row, resulting in the planar, rectangular parallelepiped structure. The procedure of slicing the substrate into rows greatly improves processing as compared to the alternative of processing each head individually. One disadvantage of this procedure is that the step of slicing the substrate into rows for lapping using a row tool is an extra step that increases manufacturing time and costs.
A further disadvantage of the conventional thin film magnetic head having a planar, rectangular parallelepiped structure is that, despite time consuming and expensive planarization processing, the planar structure does not furnish an optimum contact of the magnetic tape media.
What is needed is a thin film magnetic head planarization technique that avoids planarization of each head individually. What is further needed is a thin film magnetic head fabrication technique that produces a thin film magnetic head having an improved tape contact.
A process of chemical-mechanical contouring (CMC) using a stair-step etch involves formation of an elevated layer of substrate overlying a device, in the illustrative example a thin-film magnetic head. The elevated layer of substrate is formed into a stair-step structure with the height and width of the stair-steps selected to attain a predetermined shape and size.
In accordance with one aspect of the present invention, an apparatus includes a substrate, and a wear surface coupled to the substrate. The wear surface has a form of a bump. The bump has a radius of curvature controlled to within 0.5 mm.
In accordance with another aspect of the invention, a thin film magnetic head structure includes a substrate having a planar surface and a plurality of magnetic heads laterally distributed on the planar surface of the substrate. The individual magnetic heads include a plurality of magnetic poles and have a head form that is raised relative to the planar surface of the substrate. The planar surface transitions to the raised head having a radius of curvature controlled to within 0.5 mm. The thin film magnetic head structure further includes an insulator layer formed generally overlying and extending lateral to the magnetic poles on the surface of the substrate, and a dielectric layer formed generally overlying the insulator layer and the magnetic poles overlying the surface of the substrate. The dielectric layer is formed into a smooth, defined shape with substantial uniformity so that radius of curvature is controlled to a defined tolerance among the plurality of magnetic heads.
In accordance with a further aspect of the invention, an apparatus includes a finished thin film substrate including a plurality of magnetic thin-film head devices and a substantially smooth, curved surface overlying ones of the plurality of magnetic thin-film head devices. The magnetic thin-film head devices have a head structure that is raised relative to a planar surface of the thin film substrate. The planar surface transitions to the raised head having a radius of curvature controlled to within 0.5 mm. The surface of the devices has a defined shape with substantial uniformity so that radius of curvature is controlled to a defined tolerance. The apparatus further includes a magnetic pole and a hard frame in the magnetic thin-film head devices. The magnetic pole and the hard frame extend to the thin film substrate planar surface. The substantially smooth, curved surface overlying the plurality of magnetic thin-film head devices is stair-step etched and chemical-mechanically contoured using a slurry including an oxygen-rich etchant and a solid abrasive material. The slurry being positively selective of the hard frame in comparison to the magnetic pole.
In accordance with another aspect of the invention, an article of manufacture includes a finished thin film substrate including a plurality of thin film magnetic heads, and a substantially smooth, curved surface overlying ones of the plurality of thin film magnetic heads. The magnetic thin-film heads are raised relative to a planar surface of the thin film substrate. The planar surface transitions to the raised head having a radius of curvature controlled to within 0.5 mm. The smooth, curved surface is at least partly formed of a dielectric layer and is uniform on the substrate so that the surface of the devices have a defined shape with substantial uniformity so that radius of curvature is controlled to a defined tolerance.
In accordance with a further aspect of the invention, a thin film processing method includes fabricating a finished thin film substrate including a plurality of magnetic thin-film head devices, and stair-step etching the head structure. The resulting individual thin-film head devices have the form of raised bumps with a plurality of stair-step edges. The magnetic thin-film head devices having a head structure that is raised relative to a planar surface of the thin film substrate. The method further includes chemical mechanical contouring (CMC) the thin film substrate subsequent to the fabrication step to smooth the stair-step edges of the raised bumps to form substantially smooth, curved surfaces.
In accordance with a still further aspect of the invention, a thin film processing method includes fabricating a finished thin film substrate including a plurality of thin film magnetic heads, stair-step etching the insulating frame of the individual thin-film heads, and chemical-mechanical contouring the heads. The magnetic thin-film heads are raised relative to a planar surface of the thin film substrate. The raised thin-film heads include a magnetic yoke, and a coil encircling the magnetic yoke. Magnetic poles are coupled at polar ends of the magnetic yoke and separated by a gap. An insulating frame encases and mutually insulates the magnetic yoke and the coil. The magnetic yoke and coil are centrally located within an individual thin-film head. Stair-step etching of the insulating frame results in the centrally located magnetic yoke and coil underlying a raised portion of the insulating frame. Portions of the individual thin-film heads lateral to the magnetic yoke and coil are etched to form depressions between the individual thin-film heads. Chemical mechanical contouring (CMC) of the thin film substrate subsequent to the fabrication step forms a substantially smooth, curved surface overlying the individual thin film magnetic heads.